Man and machine
I just built a computer. First time I ever did that. Now I'm installing Windows Vista. First time I ever did that, too. So far so good.
The tricky bit came when I was installing Windows XP -- I have an upgrade version of Vista, so I had to install XP first. Turned out the new hard drive wasn't properly recognized by old-school XP (it's a newfangled SATA drive, don'tcha know), and the only way to load drivers for it was from a floppy disk. So I had to take a floppy drive out of an old computer -- this is why I never get rid of anything -- install it in the new one and cross my fingers.
Oh yeah, and change a BIOS setting. Then, at the proper moment, change it back.